There's several mixers that have cue abilities: the Pittsburgh Lifeforms System Interface, the TEX MIX system from Tesseract, ADDAC's 807 system, and so on...basically, anything that has an AUX send will allow you to do a cue mix, but you might need an extra headphone amp module for use with those. Ladik's M-053 can also be used to split a cue mix out of a mono or stereo bussed signal with an additional headphone amp.
-- Lugia
Not to nit-pick you, but an aux send isn't always cue friendly. The aux send has to be tapped pre-fader/pre-mute to serve as a cue. On most Mackie boards, there's a switch that makes one or two aux sends pre-fader/pre-mute for example. If I remember correctly, you can also monitor the mute bus... anything that is muted can be selected for monitoring.